Vision/Image - Cal Flashcards
Light is ___(bent, focused) as it progresses through refractive structures of the eye
refracted
A receptor ___ is produced when light strikes the retinal photoreceptors of the eye
potential
The neural layer of the retina processes visual data, then sends nerve impulses into axons that comprise the
optic nerve
Impulses are conveyed to the ___, and on to the cerebral cortex where they are interpreted as images
thalamus
Refraction (bending) of light occurs when light rays traveling through a transparent substance pass into a second transparent substance with a
different density .
This is because the light travels at different speeds in materials of different densities
A beam of light travels in a uniform front after being produced
When the beam travels toward a biconvex lens, One part of the beam arrives at the lens before the rest of the beam. Those light rays enter the lens first, and ___. But the remaining parts of the beam continue at the original, faster, speed until they, too, encounter the lens
slow down
The different arrival times, and consequent different times of slowing, cause the beam to refract (bend)
Slide 4-8
light converges, and is focused by the ___ lens
convex
concave lens causes the light to?
diverge
slide 8
Light rays entering the eye are refracted by the __ and ___
cornea and the lens
Most refraction occurs at the ___, with the lens providing much of the remainder.
cornea
The aqueous humor and vitreous body are minor participants in light refraction
Images formed on the retina are inverted.. meaning?
Upside down
Show left-to-right reversal
The brain learns early in life to coordinate visual images with the orientation of objects, so the inverted images are not a problem
Cool
Light rays reflected from objects ___than about 20 feet from the viewer are essentially parallel
further
At this range (>20 ft) the ciliary muscle is reasonably ____, and the lens is fairly flat
relaxed
Light rays reflected from objects closer than about 20 feet from the viewer are?
not parallel
At ranges closer than 20 ft, The lens must be ___ to properly focus the image
thicker
In accommodation, The ciliary muscle ___, reducing tension on the suspensory ligaments, and allowing the lens to assume a more spherical shape
contracts
The increase in the curvature of the lens for near vision is called?
Accomodation
Absent tension on the lens via the suspensory ligaments (zonular fibers), the lens assumes a ___ shape
convex
When the ciliary muscle is relaxed, the ___ acts like a spring pulling on the lens through the suspensory ligaments, causing the lens to become less convex.
choroid
When the ciliary muscle contracts, it stretches the choroid, releasing the tension on the lens and the lens becomes ____
thicker
the minimum distance from the eye that an object can be clearly focused with maximum accommodation
Near point of vision
The lens loses elasticity with aging, and therefore also loses its ability to accommodate. The loss of elasticity of the lens with age, and the accompanying results, is called
presbyopia
begins in the mid-forties: people who have not previously needed glasses begin to need them, and those who already wear glasses need bifocals
Presbyopia
The normal eye is termed
emmetropic
It refracts light rays from an object ___ away, such that a clear image is formed on the retina
20 feet (6 meters)
Refraction abnormalities prevent emmetropic eyesight from always being the case, as in . . .
Myopia (nearsightedness)
Hyperopia
(farsightedness)
Astigmatism (irregular curvature of the cornea)
Myopia
Hyperopia
Astigmatism
nearsightedness
farsightedness
irregular curvature of the cornea
occurs when the eyeball is too long relative to the focusing power of the cornea and lens
myopia
The image is focused in front of the retina
myopia
The condition may be due to an elongated eyeball or thickened lens
Correction is by use of a concave lens
myopia
occurs when the eyeball is too short relative to the focusing power of the cornea and lens
hyperopia
The image would be focused behind the retina
hyperopia
The condition may be due to a shortened eyeball or thin lens
Correction is by use of a convex lens
hyperopia
due to an irregular curvature of either the cornea or the lens
Astigmatism
The result is that parts of the image are blurred or distorted, and out of focus
Astigmatism
Correction is by use of a lens that rotates the axis of the light going into the eye
Astigmatism
When the pupil is ___, light rays that are allowed to enter the eye through the small opening are more parallel than when the opening is large
small
Part of the overall accommodation mechanism is ___ of the circular muscles of the iris to constrict the pupil, which occurs simultaneously with changes in the thickness of the lens
contraction
Many animals see one set of objects out of one eye, and another set of objects out the other eye
In humans, both eyes focus on only one set of objects, resulting in
binocular vision.
Binocular vision provides depth perception, and three-dimensional perspective
results when light rays from an object strike corresponding points on the two retinas, but each eye sees the same image from slightly different angles
Binocular vision
The brain fuses the two slightly different images delivered by each eye, providing (literally “seeing solid”)?
stereoscopic vision
As we move closer to an object the eyes must rotate ___ in order for the light rays from the object to strike the same point on both retinas
medially
the medial movement of the two eyeballs so that both are directed toward the object being viewed
Convergence
The outer segments of rods are
Those of cones are
cylindrical, or rod-shaped
tapered, or cone-shaped
The names rod and cone were assigned during the 1830’s based on the shape of the cells when viewed in the microscope
The two types of photoreceptors are not evenly distributed in the retina
Rods and cones
most highly concentrated in the central fovea (identified as “cone peak”), and dramatically decrease in density moving away from the fovea
Cones
Cones are most highly concentrated in the
central fovea
Rods are most highly concentrated in a ring around the
foveal pit.
Although there are no rods in the ___, where rods are present in the retina they are generally more densely concentrated than cones
fovea
The optic disc (blind spot) is?
receptor free
The outer segment is the end of the photoreceptor next to the
pigmented layer
It is in the ____ that light energy is transduced into a receptor potential
outer segment
The ____ of rods and cones are layered to increase the surface area available for trapping light
outer segments
The___ of each cone consists of folds, similar to a long pleated fabric
outer segment
The tip of the outer segment of each rod contains a stack of ___ piled up like coins in a wrapper, near the base the membrane is folded like it is in cones
discs
Outer segments of both rods and cones are easily destroyed by light, and are sloughed off at the tip, then the fragments are phagocytized by
pigment epithelial cells
Phagocytic activity occurs in a ___ rhythm. Rod tips are phagocytized in the morning after first exposure to light. Cone phagocytosis is triggered by darkness, and occurs at night.
circadian.
Turnover of outer segments is fairly rapid
The inner segment contains:
Cell nucleus
Golgi apparatus
Mitochondria (many)
The ____ end of both rods and cones expands into a synaptic terminal containing numerous synaptic vesicles
proximal
colored, integral proteins in the plasma membrane of the outer segment of rods and cones
Photopigments
Photopigments undergo structural changes when they
absorb light
Photopigments associated with vision contain two parts:
Retinal, a derivative of vitamin A formed from carotene
Opsin, which is a glycoprotein
a derivative of vitamin A formed from carotene
Retinal
a glycoprotein
not very specific I know…
Opsin
The photopigment in rods is?
…which absorbs blue to green light most effectively
rhodopsin
retinal + opsin =
rhodopsin
There are three different cone photopigments, one in each of three types of cone, each having a different absorption maximum:
Photopsin I, 2, 3
Photopsin I
Photopsin II
Photopsin III
(yellowish absorption maximum)
(green absorption maximum)
(blue-violet absorption maximum)
More specifically, it is the ___ portion of the photopigment which is different in each of the different photopigments
opsin
Retinal is the same in all photopigments, and it is retinal which is the key in transducing light energy into
electrical signals
In darkness, retinal has a bent shape called
cis-retinal.
Opsin and retinal fit together nicely when retinal is
cis-retinal
When cis-retinal absorbs a photon of light, it straightens out to a shape called
trans-retinal
The cis to trans conversion is called
isomerization
In the straight, ___ form, opsin and retinal no longer fit, and they dissociate
trans-retinal
This dissociation sets up a series of events in the photoreceptor that eventuates in perception of the?
(ie., in seeing)
photon
After light-induced isomerization of retinal from cis to trans form, the ___ rapidly decomposes during the next few milliseconds
rhodopsin
Obviously, the photopigments must be reconstituted or vision would cease
That reconstitution of photopigments is termed
regeneration
Rhodopsin has a “normal” ___ color
reddish
In the presence of light cis-retinal is converted to trans-retinal, and the opsin, now minus the detached retinal, becomes
colorless
Slide 36 (sounds weird I know)
This is termed bleaching of photopigment
An enzyme called ____converts trans-retinal back to cis-retinal
retinal isomerase
The ___ can now rebind to the opsin, reforming a functional photopigment
cis-retinal
This is called regeneration
Photopigment bleaching, and ___ occur in the eyes
regeneration
When one is in the light, photopigment is bleached. At the same time, other molecules are being
regenerated
Regeneration is too slow in daylight to keep up with bleaching in the rods, so __ contribute little to daylight vision
rods
___ photopigments do regenerate rapidly enough that some cis form is always present
Cone
Dark adaptation occurs when photopigments are able to regenerate in the dark without being bleached by light. It takes about 30 to 40 minutes for bleached ___ to fully regenerate, which is the amount of time it takes to become dark adapted
rhodopsin
Adaptation to sudden light takes only a ___ as the visual system adjusts to the brighter environment by decreasing sensitivity
few seconds
The momentary dazzling that is experienced when one moves from darkness into bright light is caused by the strong stimulation of both ____ and the large amounts of photopigments that are broken down almost instantaneously, thereby producing a flood of signals
rods and cones,
an inability to distinguish between certain colors, and results from the absence or a deficiency of one of the three cone photopigments
Color blindness
The most common OF color bliness type is ___ color blindness, in which a photopigment sensitive to red light or to green light is missing
It is generally an inherited trait.
red-green
Slide 42
What do you see
this is an inability to see well at low light levels
nyctalopia
Typically caused by prolonged vitamin A deficiency and the consequent below normal amount of rhodopsin, and which can also result in rod degeneration
nyctalopia
Vitamin A supplements will restore function if they are administered before degenerative changes occur
The retina processes visual signals at synapses among the various types of retinal neurons. Some visual inputs are enhanced, and others are
discarded
Pathways of processing may be converging or diverging, but ____ is the general rule since there are hundreds more photoreceptors than ganglion cells
convergence
Many rods (6 to 600) synapse with a single ___, but a given bipolar will generally synapse with only one cone
bipolar cell
The convergence of many rods into a single bipolar cell increases light sensitivity of rod vision, but decreases the ___ of the image
acuity
Cone vision is less ___, but has a higher acuity
sensitive
Horizontal cells and ___ cells attenuate the differences between parts of the retina that are strongly stimulated and parts that are less stimulated, as well as assist in the differentiation of colors
amacrine
Slide 48, 49
low res
Axons of the ____ cells provide output from the retina to the brain. They exit the eyeball as the ____
retinal ganglion
optic nerve
Axons of the optic nerve pass through the ____, where some cross to the opposite side, and some do not cross
optic chiasm
Upon passing through the optic chiasm the axons are now considered to comprise the ___.
optic tract
After optic tract, they enter the brain and terminate in the ____ of the thalamus
lateral geniculate nucleus
There (in lateral geniculate nucleus ) they synapse with neurons having axons that form the optic radiations, which project to the primary visual area in the ____ of the cerebral cortex
occipital lobes
The ____ of an eye is everything that can be seen by that eye
The visual field
Due to the placement of our eyes, the two visual fields overlap, which is the field of
binocular vision
The visual field of each eye is divided into two regions:
Nasal (central) half
Temporal (peripheral) half
For each eye, light rays from an object in the nasal half of the visual field fall on the ___ half of the retina, and light from an object in the temporal half of the visual field fall on the ___ half of the retina
temporal
nasal
Further, due to the pattern of crossing over or not crossing over at the optic chiasma, visual information from the right half of each visual field is conveyed to the___side of the brain
left
(and visual information from the left half of each visual field is conveyed to the right side of the brain)
Slide 54, 55
This is because the axons from the temporal half of each retina (do or don’t) cross, but continue directly to the lateral geniculate nucleus of the thalamus on the same side
DO NOT
Temportal half doesn’t cross
Slide 56
For each eye, light rays from an object in the nasal half of the visual field fall on the temporal half of the retina, and light from an object in the temporal half of the visual field falls on the ___ half of the retina.
nasal
DUPLICATE SLIDE 57
Further, due to the pattern of crossing over or not crossing over at the optic chiasma, visual information from the right half of each visual field is conveyed to the left side of the brain, and visual information from the left half of each visual field is conveyed to the __ side of the brain . This is because the axons from the temporal half of each retina do not cross, but continue directly to the lateral geniculate nucleus of the thalamus on the same side
right
DUPLICATE SLIDE 57
Axon collaterals of retinal ganglion cells project to the ___ where they are involved in circuits that govern constriction of the pupils and coordination of head and eye movements
midbrain
Collaterals also go to the ___ of the hypothalamus which establishes circadian rhythms based in part on impulses of light perception from the eyes
suprachiasmatic nucleus
Optic radiations are the projection of axons from the ___ to the primary visual area of the cortex on the same side
thalamus
Loss of vision in an otherwise normal eye
Amblyopia
caused by either no transmission or poor transmission of visual stimulation through the optic nerve to the brain during early childhood or for a sustained period thereafter due to strabismus (cross-eyes, or eye misalignment), anisometropia (one eye significantly near/far sighted) cataract, trauma, etc
Amblyopia
Detection in early childhood increases the chance of successful treatment (20/20 eye chart screening is insufficient)
Amblyopia
Sometimes called “wandering eye” or “lazy eye” but the term is inaccurate since there is no “laziness” of the eye. “Lazy brain” would be a more accurate term. The term “lazy eye” is further imprecise because “lazy eye” is also used for strabismus
Amblyopia
A number of different and separate systems (probably at least three) within the cerebral cortex operate to process and interpret visual signals:
One system process information related to the shape of objects
One system processes information about the color of objects
Another system processes information about movement, location, and spatial organization
A number of different and separate systems (probably at least three) within the cerebral cortex operate to process and interpret visual signals:
shape of objects
color of objects
movement, location, and spatial organization
